water heater relief (2x) ... root cause help?

[dnewton3]

About 3 weeks ago, I went downstairs and found that the water heater had relieved pressure; water all over the floor and even up on the walls near the location. I assumed that either the T&P was bad (most typical cause) or that the gas valve had stayed on too long (less likely, but possible). So I replaced them both. The tank looked good inside from what I could tell; very little debris or sediment. I used a lit match to check the smoke trail and made sure the vent pipe had a good updraft. Seemed fine after repairs, and so thought nothing of it.

This morning, the same thing happened. I was on the computer and heard the rush of steam and pressure. Ran downstairs and saw this (photo 1).

Now I'm perplexed. I am digging deeper. So I pulled the angled vent pipe and looked up the exhaust; it's clear as a bell (photo insert 2). I can see very good daylight at the top. I also went outside and checked the vent pipe above the roof; no damage or obstructions. The angled pipe is also clear; can see reflected light from end to end.

So, even after confirming no vent obstructions, and replacing both the T&P and gas valve itself, the failure mode had reoccurred. We've lived here for 8+ years and never had an issue until now.

I am at a loss ... Any suggestions?

 

[Sequoiasoon]

Do you have an expansion tank on it? If not you should. They go bad and many T&P assumed failures are actually from the expansion tank. If it can't expand somewhere it will expand out through T&P.

I believe it's code for a long time to have a potable water expansion tank on the cold water side.

Same thing happens to boilers.

 

[dnewton3]

No expansion tank.

But why the two failures now, after 8 years of not having one???

Is it possible we're getting supply pressure surges (we're on city water)?

 

[Inked]

2 months ago the pressure relief valve on my tank started blowing off several times a day. Thought the valve was going bad. Plumber buddy asked if I had an expansion tank. Never had one in 30 years living here. He suggested I try installing one. I did and no issues since.

Edit: Have you checked your water pressure inside the home by way of your outside water faucet? I ask because your pressure regulator coming into the house may be failing as well.

 

[walterjay]

Get an expansion tank.

 

[Sequoiasoon]

Many new water meter if they have done any work around have check valves in them. Mine got upgraded a couple years ago and now has it.

Prior to that you could hear water flow and see meter spin backwards/surge depending on water demands in the area (like sprinklers).

 

[dnewton3]

Some additional info ...
I just looked closely at the top of the water heater and took this picture. It appears to me that it's getting too hot. Look at the little plastic collars around the inlet/outlet ports. The collars are melted, as if hot gases are rolling out of the vent collector. To me, this indicates I'm seeing a temperature issue and not a pressure issue. Am I wrong? If this is temp related, after replacing the gas valve, and assuring the vent pipe is very clear, what is going on ????

Also, while I don't have a pressure gauge in my home, my neighbor does. I just talked to him and he says that we generally only get about 40psi from our utility. We live way up on a hill, and so the pressure is never high.

 

[Inked]

By the picture of those collars and vent I’d say you’re correct. Your relief valve was doing its job and it’s a temperature problem, not a pressure problem. What is your thermostat set for as opposed to what temp you have coming out?

 

[JohnnyG]

No expansion tank.

But why the two failures now, after 8 years of not having one???

Is it possible we're getting supply pressure surges (we're on city water)?

Have you recently installed a backflow preventer, or pressure regulator? Did the city do something at the meter to prevent backflow?

 

[dnewton3]

By the picture of those collars and vent I’d say you’re correct. Your relief valve was doing its job and it’s a temperature problem, not a pressure problem. What is your thermostat set for as opposed to what temp you have coming out?

The thermostat at the gas valve is set "midline" (midrange). Same as it's always been.

 

[Bailes1992]

Do you guys have electrical immersion heaters fitted in your cylinders too? There's no chance the controls have failed on?

 

[dnewton3]

Have you recently installed a backflow preventer, or pressure regulator? Did the city do something at the meter to prevent backflow?

Nothing installed by me, or the utility.

 

[Inked]

So to summarize thus far:

- You replaced the gas valve and T&P
- Your tank looks fine with very little sediment
- Your thermostat is set correctly
- Belief at this point is that it’s a temp problem and not a pressure problem as seen by the damage to those collars (I would still get an expansion tank though)
- Nothing recently installed

Just a guess but I would now be looking at the possibility of a bad thermostat that is not regulating how long your burner is running and thereby causing the temp to rise to a level that the pressure relief valve is opening. If it were me I’d shut it down immediately if you haven’t already.

 

[Dave P.]

Me, I'd be getting a new hot water heater. Especially if you spend much time on that treadmill!

 

[dnewton3]

So to summarize thus far:

- You replaced the gas valve and T&P
- Your tank looks fine with very little sediment
- Your thermostat is set correctly
- Belief at this point is that it’s a temp problem and not a pressure problem as seen by the damage to those collars (I would still get an expansion tank though)
- Nothing recently installed

Just a guess but I would now be looking at the possibility of a bad thermostat that is not regulating how long your burner is running and thereby causing the temp to rise to a level that the pressure relief valve is opening. If it were me I’d shut it down immediately if you haven’t already.

Decent summary.

Yes; it came off-line immediately after it happened. I have two water heaters that serve the house. They are on isolated circuits, but there is a "cross-over" which I can open to make either one serve the entire house. I just shut off the in/out water to the offending unit (gas fired, in this case), open up the bypass crossover, and let the other heater (electric) do its job. Which is also why I doubt it's a water pressure issue; the other water heater has not blown off its T&P either time.


I am beginning to think I need to replace the water heater itself. It's definitely not the vent; it's nothing but daylight in that exhaust pipe. After replacing the gas valve and the T&P, about the only root cause left is the heater body itself. Maybe there's something wrong internally that I cannot see, but is affecting the performance by causing overheating events. The melted collars lead to this conclusion.

 

[Inked]

If it’s ever determined what the root cause was I’d like to know (learn).

 

[RhondaHonda]

Nothing to comment but I have the same leg lamp in the FRAGILE (Fra-Gee-Lay) boxes and got a good laugh seeing them.

 

[We're Metals]

Dude, just replace it

 

[shortyb]

Bad t-stat. Is it over 8-10 years old? Time for a new, shiny one.

 

[oldcodger]

Go ahead and put an expansion tank in and try it out. No matter what you do you need one. You will need a pressure gage to set the pressure on the expansion tank.
I had some of the same symptoms you have when the utility installed a check valve at my meter and did not tell me about it. I went through quite an experience with hot water faucets leaking and my hot water tank started to leak. When I put a new tank in the pop off valve started leaking. I finally figured it out. If the utility had simply notified me about the new check valve it would have made things easier.